KR100237809B1 - Process of n-methylmorpholine-n-oxide powders by a fluidized bed spray drying - Google Patents

Abstract

The present invention relates to a method for producing NMMO hydrated powder having a water content of 5 to 15% by weight through a step of spraying and fluidizing a liquid NMMO solution in a powdering apparatus. The manufacturing method of the NMMO hydrated powder of the present invention is simpler in process than in the conventional method, consumes less energy and decomposes the solvent.

Description

Process for preparing N-methylmorpholine-N-oxide hydrated powder using fluidized bed spray drying.

The present invention relates to a method for preparing N-methylmorpholine-N-oxide (hereinafter referred to as NMMO) hydrated powder, and more particularly, to a water content of 5 to 15 weight by spraying and drying an NMMO solution in a fluidized bed injector. It relates to a method of producing% NMMO hydrate powder. The NMMO hydrated powder prepared according to the present invention can be used as a solvent of cellulose in producing cellulose fibers or cellulose films.

A method of dissolving cellulose by using an amine oxide includes a method of using an amine oxide in a liquid phase and a method of using a solid phase.

A method for preparing a cellulose solution using a liquid tertiary amine oxide solvent is described in US Pat. No. 2,179,181 to Graenacher et al., And methods for preparing solutions more efficiently and economically continue. For example, US Pat. Nos. 4,142,913, 4,144,080, 4,196,282 and 4,246,221, European Patent 356,419 and WO 94/06530 disclose tertiary amine oxides in which cellulose cannot be dissolved. A method for producing a cellulose solution by a vacuum distillation method in which a cellulose is dissolved is disclosed by first swelling cellulose in an aqueous solution (cellulose non-solvent) to obtain a slurry, and then removing excess water contained in the slurry by distillation under reduced pressure. However, the cellulose manufacturing method is not only complicated because the solution is prepared through a long time under reduced pressure distillation, but also has a problem of discoloring the solution due to thermal decomposition of the solvent and cellulose and waste of time and energy due to long time under reduced pressure distillation. have.

On the other hand, US Patent No. 4,416,698 discloses a method for preparing a cellulose solution using a solid amine oxide solvent. In this patent method, a cellulose solution is prepared by simply mixing the cellulose powder and the solid NMMO hydrated powder, and then transferring the same to a extruder to dissolve it. However, since this method simply mixes the cellulose powder and the solid solvent, when a large amount of the mixture is prepared, the cellulose powder and the solid NMMO solvent powder are not uniformly mixed with each other to be dissolved in the finally prepared solution. Cellulose particles that are not present are disadvantageous in that a uniform cellulose solution cannot be prepared. In order to solve the drawbacks of using such NMMO solvent powder, US Pat. No. 5,584,919 also discloses a method for producing solid composite particles.

As described above, the method using the solid amine oxide powder in the preparation of the cellulose solution can be prepared by simply mixing the cellulose powder and the solid amine oxide solvent, the production time is shorter than the method using the liquid amine oxide solvent Although the process is simple and there are many advantages of low decomposition of the solvent, in the case of preparing a cellulose solution using a conventional solid NMMO hydrated powder, the cellulose powder and the NMMO solvent powder are different from each other when a large amount of the cellulose mixture is prepared. There is a disadvantage in that a uniform cellulose solution cannot be prepared because undissolved cellulose particles are present in the finally prepared solution because they do not form a uniformly mixed state. Furthermore, the conventional method of preparing NMMO powder has a disadvantage in that the process is complicated and energy loss is large because the NMMO solution is concentrated to a high concentration and then cooled and solidified and then pulverized.

An object of the present invention is to provide a method for producing NMMO hydrated powder that can be uniformly mixed with the cellulose powder to produce a highly homogeneous cellulose solution, unlike the conventional process for producing a complex NMMO hydrated powder, the process time is The present invention provides a method for preparing an amine oxide-based NMMO hydrate powder which can prepare a highly homogeneous cellulose solution by a short and simple process.

1 is a process chart for preparing the N-methylmorpholine-N-oxide hydrated powder of the present invention.

2 is an illustration of a typical diagram of a fluidized bed spray dryer used to prepare the N-methylmorpholine-N-oxide hydrated powder of the present invention.

3 is a process chart for preparing a homogeneous cellulose solution using the N-methylmorpholine-N-oxide hydrated powder of the present invention.

* Explanation of symbols for main parts of the drawings

1: tertiary amine solution 2: feed pump

3: injection nozzle 4, 4 ': air filter

5, 5 ': fan 6, 6': heat exchanger

7 fluidized bed spray drying unit 8 fluidized bed air distribution unit

9: dust collector 10: gas discharge unit

11: hydrated powder recovery unit

In order to prepare a homogeneous cellulose solution in which undissolved cellulose particles are not present, the inventors require uniform mixing of cellulose and an amine oxide solvent. This resulted in the discovery that there were no undissolved cellulose particles present in the finally prepared solution and the present invention was completed.

Therefore, the present invention,

(a) preparing a concentrated NMMO solution,

(b) spraying the NMMO solution in a fluidized bed spray dryer;

(c) fluidizing the injected NMMO solution to produce NMMO hydrated powder particles having a water content of 5 to 15% by weight.

Provided is a method for producing NMMO hydrated powder using fluidized spray drying.

The concentrated NMMO solution for use in the present invention may have a moisture content of 5 to 30% by weight, preferably 10 to 25% by weight. Such concentrated NMMO solutions may be prepared by directly concentrating the NMMO aqueous solution or may be prepared according to other conventional NMMO solutions.

The next step is to powder the prepared concentrated NMMO solution. Powdering of liquid materials includes a prill process (US Pat. No. 5,354,520), a spray dryer (US Pat. No. 3,956,521), a combined form of the spray dryer and fluidized bed (US Pat. No. 4,608,203, copper) 4,578,876) have been proposed in a variety of fields, such powdering process can be used to powder the NMMO solution in the present invention, but fine spraying of NMMO solution in the tower and using a fluidized bed Drying is most suitable. The method using fluidized bed spray drying can be used in both batch and continuous methods, and is suitable for mass production as well as small-scale production. [JF Davidson et al. (Fluidization Second Edition, Academic Press, 1985). In the present invention, the injection and fluidization steps can be performed sequentially or simultaneously.

NMMO hydrated powder prepared through the injection and fluidization step is preferably to have a water content of 5 to 15% by weight. NMMO hydrated powder having a water content of 5 to 15% by weight may be uniformly mixed with the cellulose powder in the preparation of the cellulose solution to make the overall composition uniform.

The manufacturing method of the NMMO hydrate powder which concerns on this invention is demonstrated with reference to an accompanying drawing. As shown in Figure 1, in order to prepare the NMMO hydrated powder according to the present invention, it is necessary to first prepare a concentrated NMMO solution through a concentrator, other methods and the like. It is preferable to concentrate the moisture content to about 10 to 25% by weight. The concentrated liquid NMMO solution is transferred through a delivery tube into the powdering apparatus. In order to keep the NMMO solution in solution in the spraying step, the temperature of the solution must be maintained at about 60 to 130 ° C. Using an injector, the NMMO solution is sprayed to produce fine droplets. The injected NMMO droplets become droplets containing a certain amount of moisture as the moisture evaporates. The fluidized NMMO droplets along the gas stream of the fluidized bed are then solidified to produce NMMO hydrated powder with a water content of 5 to 15% by weight. The NMMO solution undergoes rapid heat exchange with the gas by spraying and fluidized bed to partially evaporate and solidify the water contained in the solution, and the water of the hydrated powder produced according to the temperature and humidity of the gas in the fluidized bed and the residence time of the powdered fluidized bed. The content can be adjusted. The hydrated powder thus produced is recovered to complete the present invention.

On the other hand, an example of a fluidized spray tower that can be used to prepare the NMMO hydrated powder particles of the present invention is illustrated in FIG. Using the fluidized injection tower will be described in more detail the method for producing the NMMO hydrate powder of the present invention.

The liquid NMMO solution 1, preferably in a concentrator or the like, having a water content of 10 to 25% by weight, is conveyed to the injection nozzle 3 via a feed pump 2. On the other hand, the gas passing through the air filter 4 enters around the injection nozzle 3 which is warmed in the heat exchanger 6 to finely granulate the liquid NMMO solution. Gas used for this purpose is air, inert gas, etc., it is convenient and preferred to use air. The NMMO solution delivered to the spray nozzle should be maintained at about 60-130 ° C. to maintain its liquid phase. The NMMO solution maintained at this temperature is sprayed through the spray nozzle 3 into the fluidized bed of the fluidized bed spray dryer 7 at a constant speed to form fine droplets. The temperature at the injection nozzle is used in consideration of the thermal denaturation of the liquid, preferably 60 to 150 ^° C. The NMMO droplets are removed from the excess moisture by the hot gas to form droplets containing a certain amount of moisture. In addition, the gas passing through the air filter 4 'is cooled to below room temperature in the heat exchanger 6' and injected into the air distributor 8 at the bottom of the powdering apparatus to form a fluidized bed. The gases used herein may be the same gases as the gases entering the injection nozzle. The resulting NMMO droplets solidify in the fluidized bed to yield a solid NMMO powder having a water content of 5-15 wt% of interest. The resulting powder is produced by the specific gravity difference according to the size and degree of solidification of the particles are collected in the lower fluidized bed is discharged through the hydrated powder recovery unit (11). The particle size of the NMMO hydrated powder to be recovered is preferably 50 to 1000 μm, but the particle size of the hydrated powder of the present invention is not limited thereto. The finer particles are released to the outside along with the gas being discharged, which are once recovered from the dust collector (9) and re-introduced into the powdering unit, which coagulate with the insufficiently solidified particles sprayed from the injector to make the particles larger. do. The gas from which the fine particles are removed in the dust collector 9 is discharged to the outside through the external discharger 10.

The NMMO hydrated powder thus prepared is mixed with the cellulose powder to provide a highly homogeneous cellulose solution used to produce cellulose fibers, films, and separators through processors such as extruders. An example of a process for preparing a cellulose solution using the NMMO hydrated powder according to the present invention is shown in FIG. 3.

The method for producing NMMO hydrated powder of the present invention has the following advantages.

First, according to the present invention, since the solid NMMO powder is prepared directly from the liquid NMMO solution, the process is simple. In addition, since NMMO is powdered to control particle size, solid particles which are easy to transport are manufactured to facilitate transportation and easy storage.

Second, the NMMO solution used for pulverization is higher than the water content of NMMO powder containing 5 to 15% by weight of water, which is required for the final product, due to the easy removal of water efficiently according to the operating conditions in the pulverization machine. NMMO solution containing water, preferably NMMO solution containing 10 to 25% by weight of water can be used in the powdering machine. The use of NMMO solution with high water content lowers the concentration load of NMMO aqueous solution, and the higher the water content of NMMO solution is, the easier the liquefaction of NMMO solution is at low temperature, thus lowering the temperature in the delivery pipe of NMMO solution. Less and less solvent decomposition.

Third, when using a powdering device that sprays NMMO solution to remove moisture and cools in a fluidized bed, the solution is sprayed into the air through the nozzle and fluidized so that the water in the solution is solidified by rapid heat exchange. Shorter exposure time results in less degradation of NMMO.

Fourth, the NMMO hydrated powder having a water content of 5 to 15% by weight according to the powdering method of the NMMO solution can be uniformly mixed with the cellulose powder when the cellulose solution is prepared, so that the overall composition is uniform. It dissolves easily and does not produce undissolved cellulose.

Hereinafter, the content of the present invention will be described in more detail with reference to Examples, but it should be noted that the present invention is not limited only to the following Examples.

Example 1

For use as a starting material (480 g) of NMMO hydrated powder having an average particle size of 100 μm of water content of 15 wt% was introduced into a fluidized bed and fluidized by introducing 25 ° C. air. In addition, the NMMO solution having a 20% moisture content, which was concentrated in a concentrator, was transferred and maintained at 80 ° C. and sprayed at a rate of 240 g per minute through a spray nozzle maintained at 100 ° C. located at the top of the fluidized bed. This injection and fluidization treatment was performed for 5 minutes, then the injection was stopped and only fluidization was carried out for cooling. Air at room temperature was cooled to 10 ° C. through a heat exchanger as a gas for cooling and injected into an air distributor located below the fluidizer. The NMMO droplets produced by the injection were solidified in the fluidized bed by fluidizing for 3 minutes to obtain NMMO powder having a moisture content of 13% by weight and an average particle size of 150 µm. The finer particles were recovered in the dust collector and re-introduced into the fluidized bed.

The NMMO powder thus prepared was mixed with a cellulose powder having a diameter of 180 μm (manufactured by ITT, trade name: Cellunier-F, polymerization degree: 660) in a mixer to prepare a cellulose solution directly in an extruder maintained at 100 ° C.

The cellulose collected from the prepared cellulose solution had a degree of polymerization of 630 calculated from the viscosity according to the method of ASTM (D 539-51T). The change in NMMO produced during the preparation of the cellulose solution was measured by 30% NMMO aqueous solution reaching equilibrium by separating 10 g of solution from the prepared cellulose solution and immersing in 16.17 ml of distilled water for 60 minutes. Absorbance of the solution according to solvent decomposition was measured at 450 nm using a UV-Visible spectrophotometer (Model: Hewlett Packard HP8453), and the absorbance of the measured solution contained 1% NMMO in weight ratio. Absorbance of the solution (optical density of amine oxide: AOOD) is shown. The AOOD of the 50% NMMO aqueous solution used in this experiment was 0.0006, and the AOOD of the prepared solvent was 0.008. The prepared cellulose solution was very homogeneous and observed with a Zeiss polarization microscope, and the presence of undissolved cellulose particles was not observed in the solution.

Example 2

A 16% moisture content NMMO solution was transferred while maintaining at 80 ° C. and sprayed at a rate of 170 g per minute through a spray nozzle maintained at 100 ° C. located at the top of the fluidized bed. The fluidization step was performed by injecting air at 20 ° C. into an air distributor located at the bottom of the fluidization apparatus. After the injection and fluidization treatment was performed for 7 minutes, the injection was stopped and only fluidization was performed for cooling. The NMMO droplets produced by the injection were agglomerated and solidified in the fluidized bed by fluidizing for 3 minutes to obtain NMMO powder having a moisture content of 13% by weight and an average particle size of 100 μm.

The NMMO powder thus prepared was mixed with the cellulose powder used in Example 1 in a mixer to prepare a cellulose solution in an extruder maintained at 100 ℃. The evaluation method of the produced cellulose solution was performed by the same method as Example 1.

The degree of polymerization of the cellulose collected from the prepared cellulose solution was 635, and the AOOD of the NMMO solution for confirming decomposition of NMMO generated during the manufacturing process was 0.006. In addition, the undissolved cellulose particle in a cellulose solution was not observed with the polarization microscope.

The method for producing NMMO hydrated powder using fluidized bed spray drying according to the present invention is to prepare a solid NMMO hydrated powder directly from a liquid NMMO solution, shorter process time, simpler, less energy consumption and less solvent decomposition. The NMMO hydrated powder thus prepared can be used to prepare a highly homogeneous cellulose solution.

Claims (5)

(a) preparing a concentrated N-methylmorpholine-N-oxide (NMMO) solution; (b) spraying the NMMO solution obtained in step (a) in a fluidized bed spray dryer; (c) fluidizing the sprayed NMMO solution to produce NMMO hydrated powder particles having a water content of about 5 to 15 wt% A method for producing a NMMO hydrated powder for producing a highly homogeneous cellulose solution comprising a. The method of claim 1 wherein the moisture content of the NMMO solution of (a) is about 5 to 30% by weight. The method of claim 1, wherein the temperature when spraying the NMMO solution of step (b) is about 60 to 150 ^° C. The method of claim 1 wherein the spraying and fluidizing steps occur sequentially or simultaneously. 5 to 15% by weight of NMMO hydrated powder prepared according to any one of claims 1 to 4.

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